Utility vehicles typically include an internal combustion engine, which delivers power to a transmission and ultimately to a wheel for traction, and also delivers power to pressurize hydraulic fluid, via one or more pumps, to operate hydraulic tools or implements.
For example, a tractor may have three hydraulic pumps driven from the engine. A first pump may provide pressurized hydraulic fluid to charge a steering cylinder of the vehicle. A second or “main” pump is usually fixed directly to the crankshaft of the engine and may be used to charge pressurized hydraulic fluid to the loader and the backhoe hydraulic cylinders.
A third or “auxiliary” pump may generate pressurized hydraulic fluid to charge a power takeoff clutch pack and at least one hydraulic cylinder which operates a three point hitch or “rockshaft.” The power takeoff is a shaft that is rotated by the vehicle transmission and is used for supplying rotational power to tools, such as mower decks, where rotation is required.
In small utility tractors, the first or steering pump typically requires about 1.4 to about 8 horsepower, depending on steering demand, and about 22 L/min (about 6 gallons per minute) of hydraulic fluid. The second or “main” pump typically requires about 3.2 to about 21.3 horsepower, depending on demand from loader or backhoe hydraulic systems, and about 46 L/min (about 12 gallons per minute) of hydraulic fluid. The third or “auxiliary” pump typically requires about 1 to about 9.5 horsepower, depending on demand from the rockshaft circuit, and about 20 L/min (about 5 gallons per minute) of hydraulic fluid. The engine for a small utility tractor typically delivers about 25 to 50 horsepower.
When a hydraulically powered attachment such as a sweeper, snow thrower, breaker, auger or cold planer is attached to a utility vehicle, the rockshaft may not be needed, nor is it practically operable. The present inventors have recognized the desirability of diverting hydraulic fluid that would otherwise supply the rockshaft when an attachment such as a sweeper, snow thrower, breaker, auger or cold planer is used. Furthermore, the present inventors have recognized the desirability of using the circulating hydraulic fluid otherwise available to the rockshaft to improve the effectiveness and efficiency of the utility vehicle.
Hydraulically powered attachments such as a sweeper, snow thrower, breaker, auger or cold planer are typically attached to the utility vehicle loader in place of the loader bucket. These attachments may be raised and positioned using the boom and bucket hydraulic cylinders.
The present inventors have recognized that a proper balance of available engine horsepower directed to the various tractor functions at the proper time is required for best operation of the machine. For example, U.S. Pat. No. 6,672,399 assigned to Deere and Company of Moline, Ill. relates to a method and apparatus for diverting pressurized hydraulic fluid, otherwise available to a utility vehicle rockshaft system, to be used by a backhoe hydraulic system.
While the loader is in use, the transmission must necessarily also be in use simultaneously. As such, it is desirable to limit the available horsepower consumed in the operation of the loader while demands are placed on the transmission, to prevent the engine from stalling. Furthermore, it is desirable to limit the hydraulic flow to the boom and bucket circuits so that the boom and bucket do not move too fast, but move at an appropriate rate.
The inventors also have recognized that hydraulically powered attachments such as a sweeper, snow thrower, breaker, auger or cold planer are used without high demand on the transmission, backhoe, rockshaft, or steering circuits. Furthermore, the inventors have recognized that it would be desirable to utilize additional flow from tractor hydraulic systems which are sitting idle while such an attachment is in use.